1. Field of the Invention
The present invention relates to a miniature cylindrical radial-gap type rotary electric machine having improved mounting accuracy of stator yokes and handling such as assembly thereof and, more particularly, to a bobbin that allows positive positioning between the stator yokes and a rotary electric machine adopting the bobbin.
2. Description of the Prior Arts
Generally, an inner rotor type brushless DC motor has stator yokes arranged on the inside of a case of the motor and a rotor rotatably arranged at the center portion of the stator yokes wherein the stator yokes are excited to rotatably drive the rotor. A stator yoke comprises a salient pole composed of a plurality of laminated thin plates which is fitted into a bobbin and magnet wires wound around the bobbin. The stator yokes, thus fabricated are predetermined positions inside the case of the motor.
The inventor of the present application proposed in Japanese Patent Application No. 178687/1997 a rotary electric machine wherein resin is injected in between a case of the motor and a stator portion to form them into one piece. This proposal brings such advantages that filling of the resin allows the stator to be secured to the case with the result that assembling accuracy is improved and durability is increased.
However, in the above proposed motor a plurality of stator yokes must be secured to the inside of the case with accuracy, thus resulting in much labor and time for the assembly. For example, when a plurality of stator yokes are mounted on the inner surface of the case, if the center of the assembly is dislocated from the center of revolution of the rotor, or there is a variation of a distance between the stator yokes thus mounted, then torque ripple or cogging torque shall be increased with the result that the performance of the motor will be lowered.
Furthermore, in the rotary electric machine above-mentioned wherein resin is injected in the case of the motor, the stator yokes must be positively held at predetermined positions until the resin completely solidifys. In this case, there are problems in that weak holding of the stator yokes causes displacement thereof or dislocation of the center thereof thereby reducing the efficiency of the motor.
Furthermore, if the stator yokes are arranged so closely with each other at the edge portions thereof, resin flow will be blocked thus preventing resin from being filled in the whole stator yokes from the front to the rear surfaces thereof.